A teen-age girl presented with recurrent stereotyped episodes of vertigo and ataxia and manifested constant horizontal gaze-evoked nystagmus. Cranial computed tomographic scans and metabolic biochemical screens gave normal results. The diagnosis of familial periodic ataxia was made from the family history and examination of the family members. Familial periodic ataxia is a rare disorder of cerebellar function which is inherited dominantly and has a benign prognosis. The underlying pathophysiology remains uncertain but a therapeutic response frequently is achieved with acetazolamide.